Container closures are well known in which an integral sealing ring, rather than a separate liner or gasket, provides a seal upon the top rim of the neck of a bottle or jar. Such closures, usually referred to as linerless closures or caps, are disclosed, for example, in U.S. Pat. Nos. 3,055,526; 3,203,571; 3,802,590; 3,948,405; 4,072,244; and 4,526,284, and in Austrian Pat. No. 274,657 and French Pat. No. 1,213,812. The sealing ring may be frusto-conical and extend downwardly and outwardly from an inner surface of the top wall of the closure or downwardly and inwardly from that surface. The same general seal configuration may be provided by a separate sealing ring or liner, as disclosed, for example, in U.S. Pat. No. 3,331,523.
Linerless closures are usually molded in one piece from plastic resin, such as polypropylene, polyethylene or other types of plastic material, as disclosed, for example, in the aforesaid U.S. Pat. No. 3,055,526. The rigidity of the closure and its parts may be controlled by the choice of plastic material and by the part thicknesses.